The discussion in Zigmond et al (cited below) does not mention
whether the relationship between Urbilateria and flatworms. I
would also worry about nematodes who have both a dorsal and
a ventral nerve cord.
I haven't yet read the citations, but I disagree that Saint Hillaire
had any grain of correctness in the inversion hypothesis. True,
there is a mechanism directing dorsal-ventral differentiation and
that might be shared among all metazoa, as are many genetic
systems for controlling how to build a complex multicellular body.
But you don't get a vertebrate nervous system by turning an embryo
upside down or by building an arthropod one on the wrong side
of the body! The whole neural tube idea is novel.
I think it is more like: OK, we both know top from bottom the same
way. Now where do I put things? You really put your nervous system
the bottom, below the digestive system and heart? How weird, I did
it the other way around! It takes all kinds!
hemidactylus at my-dejanews.com wrote in message
<7f821a$brc$1 at nnrp1.dejanews.com>...
>In article <3714FFB8.4F0C4294 at umich.edu>,
> Richard Norman <rnorman at umich.edu> wrote:
>> I don't remember what this thread was originally called,
>> it has scrolled off my news group, but I have found
>> some new info.
>>>It was called "CREB?". It was I who spawned it. Thank you for
>>>> "Fundamental Neuroscience" (Zigmond, Bloom, Landis, Roberts
>> and Squire, Academic Press, 1999) refers to this notion in
>> Box 2.5 on page 19, "How to turn a lobster into a vertebrate".
>>>> It attributes the notion of inversion of the dorsoventral axis
>> to E Geoffroy Saint-Hilaire in 1822. It also cites recent
>> studies on the patterning of the dorsoventral axis in the
>> "Urbilateria", a precursor and common ancestor of arthropods
>> and chordates:
>>>Was this discussed as a "flatworm ancestor"?
>>>> DeRobertis, E.M. and Y. Sasai, A common plan for dorsoventral
>> patterning in Bilateria. Nature 380:37-40(1996)
>>>> Hogan, B.L.M. Upside-down ideas vindicated. Nature 376:210-211
>>>>Thank you for the references, Richard. Geoffroy wasn't so far off the
>guess. Too bad those scientists way back when couldn't enjoy the
>techniques used today. Of course 100-200 years from now, people might
>saying similar things about the scientific greats of our time.
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